Age hardening silver of sterling or higher standard



Patented .Dec. 11, 1934 UNITED STATES AGE HARDENING SILVER F STERLING 0R HIGHER STANDARD James C. McFarland, Fort Thomas, Ky., assignor to The Wadsworth Watch Case Company, In-

corporated, Dayton, Kentucky Ky., a corporation of No Drawing. Application September 14, 1932 Serial No. 633,116

9 Claims.

The present invention relates to silver alloy of sterling standard or higher in fineness and has for an object the provision of such an alloy that may be age hardened to a degree that renders it useful in objects and for purposes for which sterling silver has never been practical or wholly satisfactory.

Another object of the invention is to pro-'- vide an alloy of this kind that may be worked cold and may be used for products or articles in which resiliency of various degrees and rigidity are highly essential.

Another object is to provide an alloy of the class described that may have its hardness increased upon drawing or age hardening far beyond the regular or standard sterling silver and which will yet contain the requisite ninety-two and one half per cent (92 /2%) or more of pure silver.

Standard or sterling silver contains ninetytwo and one half per cent (92 /2%) pure silver and seven and a half per cent (l /2%) of copper, and, as ordinarily annealed, contains copper distributed throughout the silver solid solution matrix in the form of small particles in which particles some silver is dissolved.

By heating for about a half hour'at 1350 F.

and quenching, these copper particles are dissolved and retained in a super-saturated solid solution in the silver. In this condition the silver is very soft. Upon drawing or age hardening this silver about one hour at 570 F., structur s which look like martensite, troosite, and pearlite are obtained. These effects are caused by the decomposition of the super-saturated solid solution of copper in silver; or, in other words, these effects are caused by the difference in solid solubility of the copper in the silver at the lower temperature. In this latter condition the silver is much harder than in the annealed and quenched state.

It has been found that the substitution of certain metals for some of the copper increases this hardening upon drawing or age hardening. The invention in general then relates primarily to an alloy which contains ninety-two and one half per cent (92 /2%) or more of pure silver and seven and one-half percent (7 A;%) or less of alloying metal, part of which replaces some of the copper of the heretofore well known standard sterling silver. More specifically, the invention relates to the substitution of a metal or metals for part of the copper in sterling silceptibility of the alloy to age hardening.

It has been found that aluminum, magnesium, lead, antimony or beryllium, or combinations of these may be substituted for a part of the copper with the result that increased hardness may be imparted thereto to the extent that articles of jewelry such as watch cases, clasps, etc., and of flat ware of various kinds that require considerable rigidity and/or resiliency may be made from the alloy of the invention instead of from plated ware, thus offering a new field of utility for solid silver of standard sterling fineness.

It is to be understood that certain alloys containing less than ninety-two and one-half percent (92 /2%) pure silver can be made in Various degrees of hardness, but that they are not generally acceptable even in moderate price markets because they are of less than sterling fineness. Numerous alloys of various kinds can also be made with such a degree of hardness or brittleness that the cold working operations of cutting, forming, stamping, etc., cannot be performed on them.

One alloy of the present invention is made by substituting aluminum in percentages ranging from one-tenth of a per cent (.1%) to five per cent (5%). These alloys would then be represented by 92.5% silver, 7.4% copper, and .1% aluminum, and ranging upward in increasing percentages of aluminum with corresponding decreasing percentages of copper until an alloy containing 92.5% silver, 2.5% copper, and 5% aluminum, is reached. All of these alloys may be worked cold, and they show some slight increase over sterling silver in hardness for the lower percentage of aluminum while the upper percentage of aluminum is the highest one that can be worked cold. The maximum hardness obtainable from regular sterling silver is about 68 Rockwell B while the preferred alloy of the present invention will harden to about 84 Rockwell B. The higher aluminum alloys will harden up to about 94 Rockwell B. These can all be worked cold in a very satisfactory manner.

As previously indicated the present invention is concerned particularly to the production of alloys of silver that are of at least sterling fineness, i. e., contain at least 92.5% of pure silver and which are capable of age hardening, after fabrication in the usual or accustomed manner, to a greater degree of hardness than standard sterling silver. 'Articles made from the alloy of the invention are thus of sterling fineness and take place with precious metal objects but have the age hardening properties t at impart a superior resiliency and hardness thereto. Noncircular watch cases which depend upon resiliency of the metal instead of threads to hold them together, are advantageously made of the herein described alloy. This is wholly impractical in standard silver. Silver articles that were of necessity made of plated or filled metal may be made of the alloy of the invention without sacrificing strength or utilitarian properties of the article. The alloys of the present invention are considered desirable or preferable on the basis of their relatively greater hardness upon age hardening, over that of age hardened standard sterling silver. The aluminum and copper silver alloy is considered preferable and thereafter; the alloys which contain magnesium, lead, antimony or beryllium. Beryllium is placed last in the order of preference because special technique is required in making the alloy and this is due largely to the ready oxidation of the metal. The metals enumerated all tend to produce precipitating groups in the alloy, which exceed in hardness of the precipitating group obtained by the age hardening of standard sterlingsilver. Certain other metals have this characteristic in the alloy but the increased hardness is in some instances too small to be of great value in the jewelry and silverware art.

The alloys may furthermore be made up with or without a deoxidizing metal such as zinc, magnesium, phosphorus, etc. A preferred composition of the invention is as' follows: silver 92.5%, copper 6.3%, aluminum 1%, zinc .2%.

After the parts or articles are formed of this alloy, they are subjected to a drawing process consisting of a one hour heating at 570 F. with or without .a preliminary annealand quench from 1300 F. This drawing or hardening may be eifected by longer treatments at lower temperatures down to 150 F., or by shorter treatments at temperatures up to 750 F. It will be understood that the preliminary anneal and quench is subject to variation between 1150 F.

What is claimed is:

1. A silver alloy comprising at least 92.5 per cent silver, 0.1 per cent aluminum and the balance copper.

2. A silver alloy comprising at least 92.5 per cent of silver, 6.5 per cent copper and 1 per cent aluminum.

3. The process of making sterling silver articles of a hardness of from 80 Rockwell B to T94 Rockwell B which consists in first alloying at alloy wherein part of the customary 7.5 per cent of copper is replaced by aluminum in amounts ranging from .1 per cent to 5 per cent, then working the alloy cold to form, the article to desired shape, then age hardening the article by subjecting it to a temperature of from 150 F. to 750 F. for a period of from 6 hours to minutes.

5. The process of making sterling silver articles of a hardness of from 80 Rockwell B to 94 Rockwell B which consists in first alloying at least 92.5 per cent silver, from 7.4 to 2.5 per cent copper and from .1 to 5 per cent of a metal selected from the group consisting of aluminum, magnesium, lead, antimony, and beryllium, then fabricating the article to form by known cold working operations, then subjecting the article to age hardening heat of about 570 F. for about one hour.

6. The process of making sterling silver articles of a hardness of from 80 Rockwell B to 94 Rockwell B which consists in first alloying at least 92.5 per cent silver, from 7.4 to 2.5 per cent copper and from .1 to 5 per cent of a metal selected from the group consisting of aluminum, magnesium, lead, antimony, and beryllium, then subjecting the alloy to a preliminary anneal and quench from about 1400" F.,- then fabricating the article to form by known cold working operations, then subjecting the article to age hardening heat of about 570 F. for about one hour.

7. Sterling silver capable of age hardening to a hardness of from 84 Rockwell B to 94 Rockwell B which consists of pure silver at least 92.5%, copper 2.5% to 7.4% and aluminum .1% to 5%.

8. The process of making sterling silver articles of a hardness of from 80 Rockwell B to 94 Rockwell B which consists in first alloying at least 92.5 per cent silver, from 7.4 to 2.5 per cent copper and from .1 to 5 per cent of a metal selected from the group consisting of aluminum, magnesium, lead, antimony, and beryllium, then fabricating the article to form by known cold working operations, then subjecting the article to a. preliminary anneal and quench from about 1150 F. to 1400 F. and finally subjecting the article to an age hardening heat of about 570 F. for about one hour.

9. The process of making sterling silver articles of a hardness of from 80 Rockwell B to 94 Rockwell B which consists in first alloying at least 92.5 per cent silver, from 7.4 to 2.5 per cent copper and from .1 to 5 per cent of a metal selected from the group consisting of aluminum, magnesium, lead antimony, and beryllium, then fabricating the articles to formby known cold working operations, then subjecting the" article to a preliminary anneal and quench from about 1300 F. and finally subjecting the article to an age hardening heat of from six hours to fifteen minutes at temperatures of from 150 F. to

' JAMES C. MCFARLAND. 

